This invention relates to chain welding machines and processes and more particularly to a method of and apparatus for rotating and erecting successive chain links prior to butt-welding.
Prior apparatus and methods of producing high-strength chains fall in two principal categories. In the first, a strand of C-shaped pre-bent and interengaged chain links is, after bending, intermediately stored prior to being laid in a chain-welding machine which, in a first pass of the chain strand, welds only every second chain link. After another intermediate storage, the partly completed chain is again laid into the same chain-welding machine for final welding of the remaining chain links. The initial intermediate storage after bending and prior to welding is necessary because the output of a chain-bending machine which bends successive chain links is greater than the output of a chain-welding machine which, in one pass, welds only alternating chain links. Such manufacturing processes have disadvantages attributable to the two-fold intermediate storage and the second pass. Intermediate storage requires space, transporting of work, and involves the risk that the ends of the chain links which are not yet welded may become contaminated so that welding defects may result. Since during the second pass, two previously welded chain links are suspended in each unwelded chain link and differ therefrom by having a shorter length, a lower electrical resistance and a greater heat conductivity, the chain-welding machine must, for the second pass, be reset in terms of electrical output as well as stroke and position of its transporting tools. Despite so-called chain monitors, it is not altogether impossible for chain links to become tangled and squashed during either intermediate storage, requiring manual labor to arrange the chain strand before passage through the chain-welding machine so as to insure trouble-free running.
In the second category of manufacturing process and machine, the chain strand emanating from the chain-bending machine passes without being intermediately stored through a first chain-welding machine which in turn welds only alternate chain links. The half-welded chain strand thence passes through a second chain-welding machine which welds the remaining chain links. This uninterrupted manufacturing process, however, requires a second chain-welding machine and dictates a relatively slow operating rate of the chain-bending machine which is capable of a far greater output. Furthermore, a disadvantage common to both the aforementioned categories of manufacturing processes is that, in the chain-welding machine transport mechanism the chain strand has to be sharply accelerated and decelerated by two divisions, i.e., the length of two chain links, if the non-productive or dead time between welds is not to assume tremendous proportions. Such acceleration and deceleration, however, entail the risk that the chain link to be welded will be inaccurately positioned, resulting in a potentially faulty weld. Since a traction test can be performed only on a completely welded portion of the chain strand, traction tests cannot be carried out on chains made in either of the prior manufacturing processes until all the chain links have been welded. Should a test subsequently disclose welding faults, a relatively considerable loss of material and time results.
A manufacturing process of the type described in German Pat. Specification No. 1,023,536 substantially avoids the aforesaid disadvantages in that one chain link after another is welded, so that a synchronous operation of only one chain link welding machine with a chain-bending machine is possible. However, when carrying out this known manufacturing process, the output of conventional chain-bending machines cannot be fully exploited because the manual rotation through 90.degree. of the next chain link to be welded results in wastage of a relatively considerable amount of time. In addition, when welding small chain links, the rotation has to be performed very frequently which has a substantially adverse effect on the output.